A SLED device can provide a lot of optical power from a very limited étendue. The étendu of a light source is the product of the area from which the light emanates, and the solid angle into which the light is emitted. This is very useful when one needs to squeeze as much light as possible into applications that themselves have a small étendu. On the light receiving end the étendu is the product of the aperture area through which the light enters the application and the solid angle from which light can enter the aperture area.
The amount of light that can be coupled from a light source into an application is limited by the component with the smallest étendu. For example if an application has an étendu of 1 μm2·sr, the light source should have its power within this étendue-size, as all light that is emitted outside such an étendue is lost.
Laser diode/superluminescent light emitting diode LD/SLED devices differ greatly from LED devices: LD/SLED devices can emit 1,000 to 1,000,000 times more light into étendues of the order of 1-10 μm2·sr than LED devices. Numerous patent publications exist in the art of LD/SLED devices, for example U.S. Pat. Nos. 6,556,610; 5,974,069; 4,935,939; US2003/161371; U.S. Pat. Nos. 4,053,914 and 4,760,578.
A problem with LD/SLED devices is that they are complex and expensive to make. In the case of SLEDs, it is also desirable to minimise optical feedback and so prevent lasing as well as to provide a better beam quality beam spot. It is therefore an object to provide an improved SLED device and a method of making such devices.